This invention relates generally to a method and apparatus for reproducing an information signal and, more particularly, is directed to a method and apparatus for reproducing a color television signal comprised of a video signal and at least one of a frequency-modulated audio signal and a PCM audio signal recorded on a magnetic tape with at least one rotary magnetic head.
Information signal recording and reproducing apparatus for recording and reproducing a video signal on a magnetic tape by means of a rotary magnetic head assembly are well known in the art. For example, in a helical scan video tape recorder (VTR), at least one rotary magnetic head is rotated at a predetermined angle with respect to the longitudinal or tape running direction of the magnetic tape as the latter is advanced so as to form successive video tracks extending obliquely on the magnetic tape. With the helical scan video tape recorder, it is possible to achieve high density recording of the video signal by advancing the magnetic tape at a slow running speed and, at the same time, providing a high relative speed between the magnetic head assembly and magnetic tape. However, with known helical scan video tape recorders in which an audio signal is recorded and reproduced on an audio track extending in the longitudinal or tape running direction of the magnetic tape by a stationary magnetic head, there results a deterioration of the signal-to-noise (S/N) ratio and an increase in the wow and flutter when the speed of advancement of the magnetic tape is reduced. This, of course, results in a deterioration in the quality of the reproduced audio signal, causing the audio signal to have unsatisfactory quality when reproduced.
In order to overcome the aforementioned problem in the recording and reproducing of an audio signal by a stationary magnetic head, it has been proposed to effect the recording and reproducing of the audio signal by means of a rotary magnetic head. It has been proposed to use one inexpensive arrangement (hereinafter referred to as a Type I arrangement) to frequency modulate the audio signal and then frequency-superimpose the frequency-modulated audio signal onto the frequency-modulated video signal. The combined signal is then recorded in successive parallel tracks on the magnetic tape by the rotary magnetic head assembly. It has also been proposed to use a more expensive arrangement (hereinafter referred to as a Type II arrangement) whereby, in addition, or as an alternative, to recording the audio signal as a frequency-modulated audio signal, the audio signal is digitized as a PCM audio signal and then recorded in an overscan section of each track which is provided, for example, by increasing the tape winding angle about the guide drum assembly of the helical scan video tape recorder. In this manner, each record track obliquely formed on the magnetic tape by the rotary magnetic head assembly includes a video track section and an audio track section, the latter of which corresponds to the aforementioned overscan section. The audio signal that is recorded in the audio track section of each track is recorded as high density data obtained by processing the signal with a time axis or base compression and a complementary time axis or base expansion.
It is to be appreciated that, during reproduction, because of a better frequency characteristic, signal-to-noise (S/N) ratio, and the like, the analog audio signal reproduced from a PCM audio signal is of a higher quality than the analog audio signal reproduced from a frequency-modulated audio signal. In this manner, less expensive Type I helical scan VTRs reproduce only the frequency-modulated audio signal mixed with the video signal, while more expensive Type II VTRs reproduce only the higher quality PCM audio signal with the video signal. It is to be appreciated, however, that in the case of a recording in which only the frequency-modulated audio signal is superimposed on the video signal, only Type I VTRs can be used to reproduce the audio signal. If such a recording is reproduced by a Type II VTR, since no PCM audio signal is present, no sound will be reproduced. The converse may not be true since Type II VTRs may record both a frequency-modulated audio signal superimposed on the video signal and a PCM audio signal in an overscan section of each track, so that a Type I VTR would reproduce the frequency-modulated audio signal recorded by a Type II VTR. However, as previously stated, the PCM audio signal is of much higher quality than the frequency-modulated audio signal. Thus, if a Type II VTR only records the PCM audio signal and does not also record the frequency-modulated audio signal, the audio signal reproduced by a Type II VTR will likewise not be reproduced by a Type I VTR.